Homogeneous catalysis, transition metal clusters

Homogeneous catalysis by transition metal clusters has been reviewed from the perspective of the specific transformations.Examples of very mixed-metal clusters catalyzing processes homogeneously are collected in Table IX. As is generally the case with homogeneous catalysis, the catalytic precursor is well defined, but the nature of the active catalyst is unclear. 

Transition metal clusters are not only of interest in an academic sense, but also in a practical one. This is due to their importance in both homogeneous and heterogeneous catalysis. Small and large transition metal clusters provide manifold opportunities to study important elementary processes in catalysis. So, clarification of such famous catalytic processes as the Fischer-Tropsch-synthesis and others can be expected by synthesizing and investigating various clusters. 

Hydrogenation reactions rank among the best studied processes in homogeneous catalysis. Numerous hydrogenation catalysts, both homogeneous and heterogeneous, are known, some of which are transition metal clusters. For several cases, special properties such as high selectivity have been observed with cluster compounds. 

For a well-referenced review of this area, see G. Siiss-Fink and G. Meister (1993) Advances in Organometallic Chemistry, vol. 35, p. 41 - Transition metal clusters in homogeneous catalysis . 

The mechanism of trimerisation of acetylene on extended surfaces is thought to be similar to that observed in homogeneous catalysis using transition-metal cluster compounds.A stepwise mechanism, shown below is thought to occur ... 

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